DESCRIPTION(provided by applicant): The specific aims of this research are to examine some aspects of the receptor, ligands, and functions of human Natural Killer (NK) cells. In particular, we wish: 1. To study the formation of both the inhibitory and the lytic NK immunologic synapse. 2. To identify the ligands on target cells for the multiple lysis activating receptors on human NK cells. 3. To examine human decidual lymphocytes with respect to NK cells and Natural Killer T (NKT) cells, including their frequency, genotype, and functions (especially production of cytokines and their possible role in implantation and pregnancy) and to examine the possible relationship between Killer cell Immunoglobulin-like Receptor (KIR) haplotype variations and recurrent pregnancy loss. 4. To examine KIR with respect to a) identification of the KIR3D that differentially recognizes HLA-B2705 and HLA-B2702 and b) generation of monoclonal antibodies recognizing the unusual KIR2DL4 and KIR2DL5 that could be used in studies of their polymorphism, ligands, and functions.